Expert: Bruce E. Johnson - 11/3/2010

Question
Im building an enclosed lean-to addition onto my detached garage. it will not be climate controlled. Is it neccessary to put a frost wall around the flat work?

Answer
Hi josh, most unconditioned spaces in this case don't need a frost wall as far as I'm concerned unless you live in an area with a high water table that causes serious ground deformation when that water freezes.  Even then, if the shed is properly designed to allow for some movement of the slab, i.e. expansion joints at the abutting structures, then even if the slab moves up or down with the weather then the structure will move with it.  A shed roof is perfect for this type of connection.  You can bolt your ledger board for the rafters to be attached to the studs or masonry of the adjoining building but don't nail the end stud of the wall to the adjoining building.  Leave a half inch gap between the stud and the existing structure.  Fill that void with 1/2" foam backer rod and then caulk it with a good frost resistant urethane caulk.  When pouring your slab be sure to provide a 1/2" expansion joint between slabs. Now your only place of movement is at the bolted ledger which will pivot.  Make sure you have a good flashing tie in at the roof.  I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com